Cemented carbide intermediate therefor and process for producing the same

ABSTRACT

In a process for producing a cemented carbide by powder metallurgy, oxidizable intermediate products are treated with a carboxylic acid or anhydride thereof having a molecular weight less than 200 to prevent oxidation. The intermediate products thus obtained are also described in detail.

United States Patent [1 1 1111 3,859,056 Hara et al. 1 Jan. 7, 1975CEMENTED CARBIDE INTERMEDIATE [56] References Cited THEREFOR AND PROCESSFOR UNITED STATES PATENTS PRODUCING THE SAME 2,698,232 12/1954Golibersuch 75/204 x 75 Inventors; Akin H Masaya i 3,743,547 7/1973Green [48/63 Mitsunori Kobayashi, all of Hyogo, Japan PrimaryExaminerBenjamin R. Padgett [73] Assignee: Sumitomo Electric Industries,Ltd., A mm Examiner-R, E. Schafer Osaka, Japan Attorney, Agent, orFirm-Sughrue, Rothwell, Mion, 221 Filed: Jan. 31, 1973 & Macpcak [21]Appl. No.: 328,168

[57] ABSTRACT [30] Foreign Application Priority Data In a process forproducing a cemented carbide by Feb. 17 1972 Japan 47-16838 Powd?rmetallurgy Oxidizable intermediate PmduCtS are treated with a carboxylicacid or anhydride thereof 52 US. (:1 29/1s2.7, 29/l52.8 29/192, having amolecular Weight less than to 75/203 75/204 75 21 1 75/212: 75/221Nation. The intermediate products thus obtained are 117/100 M, 117/100B, ll7/l06 R, 117/127, also descflbed 117/161 UB, 148/63 [51] Int. ClC22c 29/00, B22f H00 17 Claims, 1 Drawing Figure [58] Field of Search75/204, 21 l, 212, 203,

75/221; 117/100 M, 100 B, 106 R, 127, 161 UB; 148/63; 29/l82.7, 182.8,192

CEMENTED CARBIDE INTERMEDIATE THEREFOR AND PROCESS FOR PRODUCING THESAME BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an improvement in processes for producing acemented carbides and to a process for producing intermediates used inthe production of cemented carbides.

2. Description of the Prior Art Cemented carbides are hard alloysprepared by a powder metallurgy method in which the main components areone or two more carbides of a Group lV-a, V-a, or Vl-a metal in theperiodic table, and one or two more powders of a Group VIII metal,present in minor proportion. Usually the carbide materials are about 70%or more of the cemented carbide.

Cemented carbides are evaluated for apparent porosity by ASTMDesignation: B276-54 (Reapproved 1965 and the transverse rupturestrength of cemented carbides by ASTM Designation: B406-70 (these werethe test procedures used to analyze the properties in the Examples).

Unless otherwise indicated, the terms in the application have thestandard powder metallurgy method provided in ASTM Designation: B243-70.

Several processes are known in the prior art for the production ofcemented carbides. The raw materials for such a process generallycomprise a powdered metal, a powdered alloy, a powdered carbide or apowdered carbide solid solution. Powdered metals or powdered alloys aregenerally formed by subjecting the oxide or hydride of the metal(s)involved to reduction or thermo-decomposition to obtain the powderedmetal(s). Exemplary of the metals used in cement carbide formationprocesses are titanium, tantalum, tungsten, niobium, molybdenum,chromium, iron, cobalt and nickel.

The powdered carbides are generally obtained by treating the oxide orhydride of the metal involved to a reduction as described above, andthen to carburization whereby the powdered carbides are obtained.Exemplary of such carbides are titanium carbide, tantalum carbide,tungsten carbide, molybdenum carbide and chromium carbide.

The powdered carbide solid solution is generally obtained by treatingthe oxide or hydride of the metal involved, the metal per se or acarbide thereof to mixing and heating in the presence of carbon, wherebya carbide solid solution is obtained such as tungsten titanium carbide,tungsten titanium tantalum carbide, etc.

Starting with one of the thus obtained powdered raw materials, whichwill hereafter often be referred to as starting powders, the first stepin the prior art processes is generally a wet mixing followed by adrying. The purpose of the wet mixing, which is usually an intensemechanical mixing in the presence of a wetting liquid or wettingsolution, i.e., a volatile lubricant, is to enable the mixture to bereadily pressed into any desirable form. The powder after drying isoften hereafter referred to as a mixture powder.

The mixture powder is pressed to provide a product which has sufficientstrength to enable it to be handled and transferred. Pressing isgenerally a cold pressing under elevated pressure, and the product afterpressing will hereafter often be referred to as a formed body.

The formed body may then be immediately subjected to final sintering toform the cemented carbide, but often is subjected to a preliminarysintering or further forming treatments. Usually the preliminarysintering is to provide strength to the formed body if it is to bemolded or processed prior to final sintering, or to activate thematerial or remove organic binder if no further molding or processingsteps are contemplated. The preliminary sintering is usually at atemperature of from 300 to 800 C. The product after preliminarysintering is hereafter often termed a preliminarily sintered body.

The preliminarily sintered body may be subjected to a forming or maythen be directly final sintered to obtain the cemented carbide. Finalsintering is at elevated temperatures as are used in the prior art,e.g., above 1,000C. and is often a vacuum sintering.

In the production of such cemented carbide, if the starting powder, thewet mixture of the starting powder, or the preliminarily sintered bodyis oxidized, the oxide film or hydroxide film formed will react withcarbon in the carbide powder or free carbon during the subsequentsintering operation used to form such materials, thereby causingdecarburization of the sintered body and resulting in an irregularcarbon content in the resulting cemented carbide. While the problem canbe encountered with the formed body, such is not usually the case sincegenerally the formed body is quickly subjected to further sintering.

In the case that the carbon content in the cemented carbide is toogreatly reduced, an abnormal phase is caused in the microstructure ofthe cemented carbide, which renders the alloy brittle and useless.However even if the cemented carbide exhibits a normal microstructure,the strength, toughness, hardness and wear resistance of the alloy areinfluenced by changes in the carbon content.

The optimum amounts of carbon in a cemented carbide are known to theart, and can be suitably determined by one skilled in the art. Forinstance, for a WC- (TiC-TaC)-Co alloy, where carbon is present ininsufficient amounts, an anomalous phase, the 'r -phase results, and thealloy becomes very brittle. On the other hand, where excessive carbon ispresent, free carbon results, also causing the alloy to become brittle.The carbon content to maintain a normal cemented carbide matrix willobviously vary depending upon the composition of the cemented carbide.Usually, however, the carbon content is within the range of from about0.06 to about 0.2 weight percent. If is preferred to control the carboncontent to within i 0.02% of the above range.

The starting powder used for forming a cemented carbide is very reactiveand easily oxidized due to the large specific surface area thereof. Thisincreased reactivity is especially encountered immediately afterpreparation or reduction or during mixing with a wetting liquid orwetting solution when the material is cleaned and activated so as to bereactive with the oxygen and the moisture in the air and the mixingsolution. Under certain circumstances, the powder becomes exothermic andis self-igniting.

The preliminarily sintered body surface, which has a large specificsurface area and is activated by the preliminarily sintering treatment,is as easily oxidized as the starting powder.

Therefore, to obtain, a cemented carbide having an optimum carboncontent it is important in the practical sense to consider that thestarting powder and the intermediate sintered body are most easilyoxidized before sintering, and decarburization of the resulting alloydue to such oxidation will be irregular.

Cemented carbides which have conventionally been produced using lowtemperature and low humidity conditions to prevent oxidation of thestarting powder and the intermediate sintered body have shown anonuniform degree of oxidation due to the influence of other treatingconditions and the treating time.

On the other hand, to carry out all the steps for producing a cementedcarbide under a vacuum or in an inert gas atmosphere to avoid oxidation,is ideal, but this is a very troublesome procedure.

Conventional procedures for treating the starting powder and theintermediate sintered product can be classified as follows:

1. A powder having the property of self-ignition was slightly oxidizedor stuck together using a fat to stabilize the surface thereof and tofacilitate handling. However, not only power thus treated but alsopowder exposed to air is oxidized to some extent. The higher themoisture contend in the air, the greater the oxidation of the powder.Accordingly, such powder must be stored in air having minimum moisture.

Although the storage of such cemented carbide starting powder underconstant conditions is possible, ensuring the powder is not brought intocontact with air during subsequent compressing and forming steps, i.e.,during supply to a press or charging into a sintering furnace, is verydifficult. The susceptability of the powder to absorb moisture and gasescan be controlled so as to be in a narrow range if the powder is treatedunder constant temperature and humidity conditions, but other treatingconditions and treating time influence the adsorption of mositure andgases. If the power is treated under conditions open to the atmospherewhere temperature and moisture vary, the amount of the powder oxidizedwill be unstable and irregular.

2. The oxidation of the powder during mixing with the solution prior topressing has been not taken into consideration, and means to solve thisproblem have been ignored. Powder oxidation during drying or thetreatment to thermally expel the mixing solution can be eliminated byprotecting the powder from exposure to air during the drying, e.g., bysubjecting the powder to vacuum drying. The powder can be protected fromoxygen between the successive pressing and sintering step by using aglove box, but this is very troublesome.

Another method of preventing the oxidation of the powder comprisescoating the surface of the powder with a lubricant such as camphor,paraffin, glycol, Zn stearate, a resin or a like high molecular weightcompound, but coating every particle of the powder is very difficult.

3. The treatment of the preliminarily sintered body has been carried outunder constant temperature and humidity conditions in a manner similarto that described for the starting powder, but this treatment could notfully prevent the oxidation of the preliminarily sintered body. Inaddition, the degree of the oxidation varies with changes in othertreating conditions and time.

The treatment of the preliminary sintered body may be carried out invacuum or under an inert gas atmosphere, but again this is a verytroublesome procedure.

SUMMARY OF THE INVENTION This invention thus has as its objects theelimination of the above described defects of the prior art and toprovide an improved process for treating the starting powder, a wetmixture of the starting powder a formed body or a preliminarily sinteredbody used in the production of cemented carbide to prevent surfaceoxidation thereof.

One feature of this invention is to contact an oxidizable material usedin the production of a cemented carbide, e.g.: (1) a Group IV-a, V-a orVIII metal, or a Group IV-a, V-a or VI-a carbide or a carbide solidsolution, immediately after preparation, i.e., a starting powder; (2) awet mixture of such metallic or carbide powders or a carbide solidsolution, i.e., the mixture powder; (3) a formed body of such startingpowders or such a wet mixture; or (4 preliminarily sintered bodythereof, with a carboxylic acid or an anhydride thereof, having amolecular weight of less than 200, in an nonoxidizing atmosphere or in avacuum, thereby adhering the carboxylic acid or the anhydride thereof tothe surface of the starting powder or the like and preventing theoxidation thereof.

In one aspect of this invention, a starting powder of the cementedcarbide, such as a powder of a Group IV-a, V-a or VI-a metal in theperiodic table, or a carbide thereof, e.g., a WC, TiC or TaC powder, ora powder of a Group VIII metal of the periodic table, is exposedimmediately after preparation, to a vaporized carboxylic acid having amolecular weight of less than 200 (or the anhydride thereof) in a vacuumor in a nonoxidizing atmosphere, to thereby adhere the carboxylic acidor the anhydride thereof to the powder surface.

In another aspect of this invention, a carboxylic acid having amolecular weight of less than 200 (or the anhydride thereof) is added toa wetting liquid or wetting solution while the starting powder and thesolution are mixed with each other prior to the production of the formedbody.

In third aspect of this invention, a carboxylic acid in the vaporizedstate having a molecular weight of less than 200 (or the anhydridethereof) is adhered to the surface of a preliminarily sintered bodyimmediately after sintering in a vacuum or a non-oxidizing atmosphere.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a plot of adheredcarboxylic acid versus molecular weight of the carboxylic acid.

DETAILED DESCRIPTION OF THE INVENTION According to one feature of theprocess of this invention, the cemented carbide starting powder hascondensed thereon a vaporized carboxylic acid having a molecular weightless than 200, or by an anhydride thereof after the step of reducing thestarting powder.

The vapor may be adhered to the reduced powder particles by introducingthe vapor into the reducing meating the vapor into the pores of thebody. As earlier indicated, this procedure is seldom necessary.

The carboxylic acid may be any unsaturated or saturated fatty acid oraromatic carboxylic acid with a molecular weight less than 200, butpreferably is one which reacts with the surface of the powder particleand not with the interior of the powder particle.

Oleic acid and stearic acid can be used, but these do not fully permeateinto the interior of a powder layer since these compounds have a highboiling point and must be heated to a high temperature to vaporize themand accordingly the molecular motion of the compounds becomes toviolent.

Therefore, the carboxylic acid or anhydride thereof must have a lowmolecular weight and a low boiling point, e.g., acetic acid, acrylicacid, propionic acid and acetic anhydride, each having the molecularweight of less than 200, provide favorable results.

An anhydride, such as acetic anhydride, having properties similar to thecarboxylic acid can also be used. However, compounds having asubstituting radical containing S,P, Cl, etc. in the carboxylic acid oranhydride material have an ill effect on the sintering treatment andshould not be used.

From the drawing it is easily seen that the lower molecular weightcarboxylic acids or anhydrides are preferred, and thus most preferredmaterials have a molecular weight of 120 150 or below.

If such a vaporized carboxylic acid or anhydride in a small amount isadhered to the surface of the powder particles, the surface activity ofthe powder particle is stabilized and successive treatments can becarried out in a short period of time to produce a uniform sintered bodyhaving a desired carbon content.

In the mixing of the starting powders with a wetting liquid solution,such as ethanol, acetone or benzene the carboxylic acid or the anhydridethereof can be added to the starting powder.

The wetting agent used can be in accordance with those used in the priorart, and any common organic liquid which is used to disperse materialscan be used so long as it does not react with either the powders orcarboxylic acid or anhydride (which will be easily apparent to oneskilled in the art). Since the purpose of using the wetting liquid is toaccomplish a physical process, i.e., to permit the powder particles tobe easily contacted with each other and cleaned, the exact choice of thewetting liquid is not overly important, and generally alcohols, ketonesand hydrocarbons (aliphatic or aromatic) are used in which thecarboxylic acid or anhydride is dispersed or dissolved.

The carboxylic acid or the carboxylic anhydride is known to be easilyadhered to a clean surface. The process of this invention is thus easilypracticed when clean surfaces are caused by the grinding of the powderduring the wet mixing treatment and the carboxylic acid or anhydride iswell adhered to the clean surface of the powder particles which iseasily oxidized and very reactive, to thereby protect the surface fromoxidation.

The effect of the adhered carboxylic acid in preventing oxidation aftera drying treatment was ascertained by empirical methods. As earlierindicated, the carboxylic acid used has a molecular weight less than200. The empirical work on the treatment of coating the starting powderwith various carboxylic acids having different molecular weight showedthat the residual carbon content of the resultant super hard alloyincreased rapidly as the molecular weight of the carboxylic acid usedexceeded 200, as shown in the drawing.

While is is not completely definite, the inventors believe thecarboxylic acid or anhydride is either adsorbed or chemically reactedwith the powder, etc. in the various embodiments of this invention.

The reason for the rapid increase of residual carbon using materials ofa molecular weight greater than 200 is believed to be that thecarboxylic acid is cracked dur ing thermal decomposition thereof, andfree carbon is apt to result.

Since the amount of carboxylic acid added to the starting powder isdetermined upon considering the number of molecules per unit surfacearea, the residual carbon amount is also increased with an increase inthe molecular weight, i.e., from the equation A= E-M-S- W/N-s, A is indirect proportion to M, and therefore A increases with increased valuesof M. Since a rapid increase of the amount of residual carbon isdetrimental in the production of the cemented carbide, the molecularweight of the carboxylic acid is accordingly, restricted to a value lessthan 200 for this additional reason.

Considering all of the above factors, the effective amount of carboxylicacid or the anhydride thereof in the mixing with a wetting solution iscalculated by the equation below:

A Amount of carboxylic acid or anhydride (g);

M Molecular weight of the carboxylic acid or anhydride;

S BET value (m /g);

S Area occupied by a molecule of the carboxylic acid or anhydride (about2 X 10 m W Amount of powder (g);

N Avogadro number;

E Safety coefficient (2 4).

Where the starting powders or preliminarily sintered body are subjectedto contact with the vaporized carboxylic acid or anhydride thereof, goodresults can be obtained by contact under condition where the carboxylicacid or anhydride is present in an amount corresponding 60 of saturatedvapor pressure.

In a further embodiment of the invention the vapor of the carboxylicacid or anhydride thereof is permeated into the fine pores of anintermediate sintered body before the final sintering treatment, wherebyit reduces the surface energy of the active inner surface of the finepores of the preliminarily sintered body, and makes the surface thereofresistant to oxidizing and prevents the formation of an oxide film andreaction with moisture in the pores, thereby preventing decarburizationand oxidation during the final sintering treatment.

The permeation of the vapor of the carboxylic acid or the anhydridethereof into the fine pores of the preliminarily sintered body iscarried out by introducing the vapor into a preliminary sinteringfurnace in which the preliminarily sintered body is contained andcontrolled the temperature in the furnace chamber to a temperatureappropriate for the permeation. Alternatively, the preliminarilysintered body may be removed from the furnace and subjected to the vaporpermeating treatment in a different container if the preliminarilysintered body is not oxidized too rapidly.

The carboxylic acid or the anhydride thereof is believed to combine withthe metal surface or the metal carbide surface, and accordingly to becapable of preventing oxidation and decarburization during sintering.This effect is probably caused by the vaporized carboxylic acidcombining with the surface of the metal or the metallic compound by achemical adsorption or chemical reaction.

If it is assumed that a pore diameter for the intermediate sintered bodymore than about 10A in diameter tends to cause excess oxidation, themaximum size of the molecule of the carboxylic acid or the anhydridethereof must be smaller than 10 A to permeate into the pore. Thisassumption turned out to agree well empirical data. Therefore, thecarboxylic acid or the anhydride thereof is restricted in accordancewith the size of the molecule and the diameter of the pores in thepreliminarily sintered body. Carboxylic acids and anhydrides thereofhaving a low molecular weight less than 200 as described in the Exampleshereinafter provide most favorable results. Carboxylic acids andanhydrides thereof having a large molecular weight cannot fully permeatinto the fine pores of the preliminarily sintered body.

On the other hand, since carboxylic acids and the anhydrides thereofhaving a high boiling point must be heated to a high temperature to bevaporized, the motion of the molecule becomes violent and accordinglythe molecules are permeated into the fine pores of the preliminarilysintered body only with difficulty. Therefore, the carboxylic acid orthe anhydride thereof must have a low boiling point and a low molecularweight. Accordingly, favorably results are obtained by the use of acompound having a molecular weight less than 200, e.g., acetic acid,acrylic acid, propionic acid and acetic anhydride as shown in theExamples.

Good results are obtained when the boiling point of the carboxylic acidor anhydride thereof which is utilized is less than about 200 C at 25 mmHg, and for most preferred results the boiling point of the carboxylicacid or anhydride thereof which is utilized should be less than about150 C at 25 mm Hg.

The carboxylic acid used may be a saturated or unsaturated fatty acid oran aromatic carboxylic acids, but must be reacted substantially onlywith the surface layer of the powder particles and not reacted with theinterior of the particles. This is another reason for using carboxylicacids of a molecular weight less than 200. Excessive reaction can easilybe determined, i.e., a n-phase will be formed or cavities will result.In such a case one should reduce the contact time, vapor pressure ortemperature of operation, or reduce two or more of such parameters.While an important factor, as a general rule one must use treatmentcondition which are obviously excessive as compared to the illustrativediscussion in the present invention to reach such an inferior product.

According to the above described three types of treatments, a cementedcarbide having a desired carbon content can be produced with ease and atlow cost.

Higher fatty acids and metallic salts thereof (oleic acid, stearic acid,laurylinic acid and their aluminum, calcium, magnesium, zinc, lead andsodium salts) are well known as rust-proofing agents for metallicarticles. The rust-proofing mechanism of these compounds is believed tobe similar to that of the lower fatty acids used in this invention, butsuch higher fatty acids are used together with an oil and fat. Besides,the molecular weight of the higher fatty acid is as large as possible toimprove the adsorbing property, so that high amounts of residual carbonare caused as shown in Figure.

Thus, the control of the carbon content and the penetration into thefine pores are impossible if a higher fatty acid is applied to theprocess of this invention. Therefore, a higher fatty acid cannot be usedfor preventing the oxidation of the intermediate sintered body and forcontrolling the carbon content of the latter and the starting powder.

The optimum amounts of carbon in a cemented carbide are known to theart, and can be suitably determined by one skilled in the art. Forinstance, for a WC- (TiC-TaC)-Co alloy, where carbon is present ininsufficient amounts, an anomalous phase, the "q-phase re sults, and thealloy becomes very brittle. On the other hand, where excessive carbon ispresent, free carbon results, also causing the alloy to become brittle.The carbon content to maintain a normal cemented carbide matrix willobviously vary depending upon the composition of the cemented carbide.Usually, however, the carbon content is within the range of from about0.06 to about 0.2 weight percent. It is preferred to control the carboncontent to within i 0.02% of the above range.

As particularly described above, the feature of this invention is to usesolely a lower fatty acid having a molecular weight of less than 200without the use of an oil or a fat, and to make use of the activity ofthe powder and the vapor permeability of the powder and the liquiddispersing property of the lower fatty acid having a low molecularweight, whereby the adsorption of the lower fatty acid to the powdersurface is increased, the oxidation of the powder is inhibited and thecarbon content of the resultant sintered body can be controlled.

Now, more specific embodiments of this invention will be described withreference to some Examples.

EXAM PLE l g of W oxide powder having a BET value of 9 m /g was reducedin an H gas atmosphere at 700 C for 20 min and cooled down to 100 C inthe H atmosphere. Then, acetic anhydride vapor was introduced into the Hgas (vapor pressure of acetic anhydride 180 mmHg.) until the temperaturedecreased to room temperature over one hour period. The metallic Wpowder thus obtained had adhered thereto 1.2 wt acetic anhydride andshowed no temperature increase upon exposure to the atmosphere.

On the other hand, metallic W powder obtained by reducing in the samemanner and cooling to the room temperature in the pure H gas atmosphereself-ignited upon exposure to air.

In the case that acetic anhydride vapor was replaced with acetic acid,propionic acid or butyric acid, the reduced metallic W powder again didnot show a temperature elevation upon exposure to air.

In this embodiment the primary criterion for successful operation isthat sufficient carboxylic acid or anhydride be present on the powder toprohibit oxidation thereof. The exact amount of carboxylic acid oranhydride which is required cannot be fixed with specificity becausethis will depend upon the severity of handling conditions to which thetreated powder will be exposed. Usually, however, greater than about 0.2weight percent of the carboxylic acid or anhydride will suffice, and inview of the relatively low cost of these materials usually from about0.5 to 1.5 weight percent will be used. Greater amounts, of course, areacceptable but generally will not be necessary and, since they aregenerally not necessary will tend to render the process economicallyless attractive due to unnecessary application of the carboxylic acid oranhydride.

The temperature, time of application and vapor pressure of thecarboxylic acid or anhydride are relatively non-critical and can beappropriately selected by one skilled in the art to bring sufficientamounts of the carboxylic or anhydride in the contact with powder. Asimple test can be used to determine if the processing conditions areacceptable, that is, if the powder obtained self-ignites upon exposureto air, greater amounts of the carboxylic acid or anhydride or longerexposure times are needed. In view of the relatively low cost of thecarboxylic acid or anhydride, it is usually easier to use relativelyhigh vapor pressures of these components and a vapor pressure of about100 to about 190 mm Hg will be used. Although very low vapor pressurescan be used, for instance, as low as about 10 mm Hg, little will begained by using such low vapor pressures considering the relatively lowexpense of the carboxylic acid or anhydride versus the extra care whichis necessary to control such low vapor pressures.

The temperature of operation is usually less than about 350 C in orderto avoid the necessity for high temperature resistant equipment, andoperation will generally proceed quite adequately at from roomtemperature to 150 C. Considering the factor of hole-time in theapparatus, usually treatment for about one-half hour to about four hourswill be used, and treatment in the general area of one hour is usuallysufficient. While very low times, for instance, in the area of tenminutes, can be used with extra care of operation, considering theeconomics of the process usually the extra effort required by theprocess operator to use such low times will be economically undesirable.

EXAMPLE 2 50 g of Co oxide powder was reduced in H gas at 600 C for min.and cooled down to 100 C in an H gas atmosphere. Then, butyric acidvapor was introduced into the H gas atmosphere (vapor pressure ofbutyric acid 50 mm Hg) until the temperature was reduced to roomtemperature over a one hour period. The obtained Co powder had 0.8 wt.%butyric acid adhered thereto and did not show a temperature elevationafter exposure to air, whereas Co powder obtained by reducing in thesame manner but cooling in a pure H gas atmosphere self-ignited uponexposure to air.

In the case that butyric acid vapor was replaced with acetic anhydride,acetic acid or propionic acid vapor the reduced Co powder also showed notemperature elevation after exposure to air.

In the case of using butyric acid, generally lower vapor pressures arepreferred, with from 30 60 mm Hg being generally used. In the case ofbutyric acid, usually from about 0.6 to 1.6 weight percent butyric acidadhered to the powder suffices for all practical commercial operations.Other conditions of operation and the factors to be considered in thetreatment are as discussed in Example 1.

10 EXAMPLE 3 parts by weight of WC powder containing 0.04 wt.% oxygen,6.11 wt.% fixed carbon and 0.06 wt.% free carbon was mixed with 10 wt.parts of Co powder containing 0.27 wt.% oxygen (500 g total powder) andthe resulting mixture was blended in a ball mill with 300 cc acetone asa wetting agent for hours at 30 C. Acetic acid in an amount of 0.4 wt.%(2g) of the powder mixture was added to the acetone prior to blending.The resultant powder mixture, after thermally expelling the acetone,contained 0.12 wt.% 0 (excluding the combined oxygen of the butyricacid) upon oxygen analysis and contained 0.38 wt.% acetic acid.

This powder mixture was further compressed at 1 ton/cm pressure andsintered at 1,400 C under vacuum for 1 hour. The sintered body obtainedshowed a transverse rupture strength of 322 kg/mm (ASTM), and contained5.49 wt.% fixed carbon and 0.00% free carbon.

On the other hand, powder mixture obtained in the same manner asdescribed above except no acetic acid was added to the acetone contained0.58 wt.% oxygen. The sintered body produced from this powder mixturecontained 5.22 wt.% combined carbon and 0.00 wt.% free carbon, andresulted in a n-phase due to the lack of carbon.

In the case that carbon powder was added to the starting powder mixturein an amount of 0.25 wt.% of the latter, the vacuum-sintered bodyobtained by similar treatments of blending, drying and forming contained5.48 wt.% combined carbon and 0.00 wt.% free carbon, and exhibited anormal microstructure but a low transverserupture strength, i.e., 247kg/mm (ASTM).

In a manner similar to heretofore discussed for the powder embodiment inExamples 1 and2, the primary criterion which the mixing embodiment ofthe present invention must meet is that sufficient carboxylic acid oranhydride be adhered to the powder during the mixing treatment. As thediscussion in the immediate proceeding paragraphs make clear, simpletests are also available in this embodiment to determine if the processconditions are effective, i.e., if a n phase results, one generallywould additional carboxylic acid or anhydride to increase the amountthereof, or would increase the process time. These conditions can beeasily determined by one skilled in the art in view of the presentdiscussion considering the fact that the process variables for thisembodiment are relatively uncomplicated.

Usually, considering the relatively low cost of the solvents used andthe relatively low cost of the carboxylic acid or anhydride thereof, ifinsufficient protection is provided the amount of carboxylic acid oranhydride thereof in the solvent is increased. Considering thesefactors, seldom would one use less than 0.2 weight per cent of thecarboxylic acid or anhydride, and generally from 0,4 to 0.6 weightpercent, based on the amount of powder mixture, will suffice to providegood results. Greater amounts of carboxylic acid or anhydride can beused, of course and in certain instances where high solvent amounts areneeded for some special process technique one would generally operatewith greater amounts of carboxylic acid or anhydride. Most usually,however, no overly significant increase in results is encountered byusing very high amounts of carboxylic ill acid or anhydride. The exactproportions can, of course, be determined by one skilled in the artdepending upon the properties of final product.

In the above example, 0.38 weight percent of the carboxylic acid wasadhered to the powder. This corresponded to 1.9 grams, and it can beseen that an extremely small amount of carboxylic acid (or, of course,the anhydride thereof) is effective for the purposes for the presentinvention. So as to provide a slight safety margin, one usually wouldnot attempt to adhere much less than 0.2 weight percent of thecarboxylic acid or anhydride, and so as to avoid excessive amounts ofcarboxylic acid or anhydride which leads to increased cost, and it willbe found for most applications that an adhered amount of about 0.3weight percent to about 0.6 weight percent is sufficient.

The temperature of operation is not overly critical and operation willgenerally be at room temperature. Seldom would any need exist to operateat temperatures greater than about 40 50 C.

The exact time of operation can vary over a wide range, and will dependprimarily upon the degree of mixing achieved. This can easily bedetermined by one skilled in the art for the exact system underconsideration.

EXAMPLE 4 90 wt. parts of WC powder containing 0.071 wt.% oxygen, 6.12wt.% combined carbon and 0.02 wt.% free carbon, 5 wt. parts of TaCpowder containing 0.04 wt.% oxygen, 6.21 wt.% combined carbon and 0.02wt.% free carbon and 5 wt. parts of Co powder containing 0.31 wt.%oxygen (500 g total powder) were mixed with each other, and the powdermixture was blended in an oscillaing ball mill with 300 cc ethyl alcoholas the wetting agent for 6 hours. at 30 0. Acrylic acid monomer in anamount of 0.5 wt.% (2.5 g) of the powder mixture was added to the ethylalcohol prior to ball milling.

Oxygen analysis of the resultant powder mixture after thermallyexpelling the ethyl alcohol by heating on a water bath showed that thecarbon content of the powder mixture was 0.09 wt.% (excluding thecombined oxygen of the acrylic acid monomer). The amount of acrylic acidadhered was 0.42 wt.% (21 g).

The powder mixture was further compressed at l ton/cm pressure andsintered at 1,450 C under vacuum for 1 hr. The sintered body obtainedexhibited a transverse rupture strength of 225 kg/mm (ASTM) andcontained 5.79 wt.% fixed carbon and 0.00 wt.% free carbon.

On the other hand, a powder mixture obtained in the same manner asdescribed above except for omitting the acrylate monomer in the ethylalcohol contained 0.36 wt.% oxygen. A sintered body produced from thispowder mixture contained an undesirably small carbon content and n-phaseformation resulted. In the case that carbon powder was added to thestarting powder mixture in an amount of 0.14 wt.% of the latter, theresultant sintered body produced by blending, drying, compressing andvacuum-sintering in the same manner contained 5.77 wt.% combined carbonand 0.00 wt.% free carbon, and exhibited a normal microstructure but alow transverse rupture strength, e.g., 194 kg/rnm (ASTM).

The same basic criteria discussed with respect to Example 3 apply toExample 4, although generally one would add slightly greater amounts ofacrylic acid to the mixture, for instance, greater than about 1.2 gramswhich corresponds to 0.24 weight percent.

EXAMPLE 5 wt. parts of TiC powder containing 0.05 wt.% oxygen, 19.95wt.% combined carbon and 0.16 wt.% free carbon, 15 wt. parts of MoCpowder containing 0.10 wt.% oxygen, 5,86 wt.% combined carbon and 0.09wt.% free carbon, and 15 wt. parts of Ni powder containing 0.27 wt.%oxygen (200g total powders) were mixed with each other, and the powdermixture obtained was blended in a ball-mill with benzine (300 cc) as thewetting agent for 150 hr. at 30 c. Propionic acid in an amount of 0.5wt.% (1 g) of the powder mixture was added to the benzine prior toblending. Oxygen analysis showed that the resultant powder mixture afterthermally expelling the benzine contained 015 M5 oxygen (excluding thecombined oxygen of the propionic acid). 0.41 wt.% (0.82 g) propionicacid was adhered to the powder mixture.

This powder mixture was compressed at 1 ton/cm pressure andvaccum-sintered at l,360 C for 1 hr.. The sintered alloy obtainedexhibited transverse rupture strength of 222 kg/mm and contained 14.88%combined carbon and 0.00 free carbon.

On the other hand, a powder mixture obtained without the addition of thepropionic acid to the benzine contained 0.61 wt.% oxygen. In order tocompensate for the low carbon of the alloy after sintering, carbonpowder was added to the mixture in an amount of 0.24 wt.% of the latter.After wet-blending, drying, compressing and sintering the carbonenriched powder mixture, the resultant sintered alloy contained 14.89wt.% carbon but exhibited a low transverse rupture strength, e.g., 196kg/mm (ASTM).

The same basic criterion discussed in Example 3 and Example 4 apply toExample 5. For propionic acid, the adhesion ratio (propionic acid added:propionic acid adhered) was about weight percent. Usually, one wouldthus provide a slight safety factor and adhere from about 0.4 to about0.8 weight percent of propionic acid to the powder. Again, little is tobe gained by using low amounts of the relatively inexpensive propionicacid, and though for certain specialized applications one might desireto use an amount approaching 0.25 weight percent, as a general rule theeconomics of the present process are not substantially benefited byusing very low amounts of the carboxylic acid or anhydride, and thetendency will be to use greater amounts so as to insure sufficientcarboxylic acid or anhydride is adhered to provide the necessary amountof protection.

EXAMPLE 6 A WC5% Co powder mixture was prepared in a ball mill,compressed and vacuum-sintered without preliminary sintering. Theresultant sintered body contained 5.90 wt.% combined carbon and 0.01wt.% free carbon.

A compressed body of the same composition was preliminarilyvacuum-sintered at 700 C keeping the vacuum at 5 X 10 mm Hg. Theresultant sintered body was then cooled to room temperature in a vacuumkept at the same level.

Acetic anhydride vapor obtained by heating the latter at 3040 C under avacuum has then introduced into the vacuum-sintering furnace (vaporpressure=20mmI-Ig) for 30 min. at room temperature. About 0.5 wt.%acetic anhydride adhered thereto. The primininarily sintered body thusobtained was taken out from the furnace and charged into a constanttemperature humidity container kept at 40C and 80% moisture. The treatedbody was again vacuum-sintered at 1,400C for 1 hr..

Another preliminarily sintered body not treated with acetic anhydridevapor was also subjected to a final sintering treatment in the samemanner.

The sintered body which was treated with acetic anhydride vaporcontained 5.82 wt.% combined carbon and 0.00 wt.% free carbon and wasscarcely oxidized. In addition, no abnormal structure or cavities wereobserved, and the physical properties were favorable.

On the other hand, the sintered body which was not treated with aceticanhydride vapor was oxidized, and accordingly contained 5.44 wt.%combined carbon and 0.00 wt.% free carbon. Further, the n-phase wasobserved in the microstructure and many cavities were present. Thepysical properties were inferior to the acetic anhydride vapor-treatedmaterial: The properties of these materials are shown in Table 1.

Table 1 sintered body treated with acetic anhydride sintered body nottreated with acetic anhydride In a manner similar to the powder and wetmixing embodiments described earlier, one skilled in the art can easilydetermine when process conditions are optimum by applying a simple testsimilar to that described in the powder mixing embodiments, i.e., theformation of an abnormal structure such as the 1; -phase or cavityformation is a clear indication that additional carboxylic acid oranhydride thereof must be introduced into the preliminarily sinteredbody. Since this operation can generally be carried out in the sinteringfurnace, it will be understood by one skilled in the art that so long asthe essential criterion of sufficient adhered carboxylic acid oranhydride is met, the exact process conditions selected are not overlycritical in the sense that certain process conditions must necessarilybe maintained within a certain range.

For case of operation, generally the vapor pressure of the carboxylicacid or anhydride will be greater than mm Hg. The use of lower pressuresgenerally increases the process time, and since this is unnecessary andcan be avoided merely by using slightly greater amounts of thecarboxylic acid or anhydride vapor little is to be gained by suchpractice. As a general rule, a carboxylic acid or anhydride vaporpressure of 200 mm Hg permits sufficiently rapid operation without thenecessity for any type of special high pressure apparatus. Of course,greater vapor pressure could be used, but this introduces an unnecessarycomplication into the process and will be seldom be used in actualcommercial practice.

In a manner similar to the earlier embodiments, the general tendency inthis embodiment will be to adhere greater amount of carboxylic acid oranhydride rather than lesser amounts. For example, seldom would one useamounts less than about 0.2 weight percent in view of the fact thatadditional amounts will provide a safety factor for any variations inprocess conditions which may inadvertently occur. Generally speaking,from about 0.3 to about 0.6 weight percent of adhered carboxylic acid oranhydride will suffice to protect the formed body for most ordinaryhandlings and treatments, but in certain instances one may, consideringthe low cost of the carboxylic acid or anhydride, wish to utilizegreater amounts.

While generally the contacting treatment can take place in the area ofroom temperature, higher tempera tures can, of course, be used, thoughseldom will a temperature greater than 350C be needed. In fact, littleis to be gained by operation for most materials outside the range ofroom temperature to about C.

The time of treating will, of course, depend upon the materials treated,the vapor pressure and the temperature of treatment, and consideringhold-time in the apparatus and the relative high cost of cementedcarbides, usually one will treat for about one third hour to about fourhours. Greater times can be used, of course, but once a sufficientamount of carboxylic acid or anhydride is adhered nothing is to begained by further treatment. On the other hand, while lower treatmenttimes can be used seldom would one treat for less than 10 minutes,considering above factors, in order to provide a safety factor.

EXAMPLE 7 Sintered bodies identical to those in Example 6 were left in aroom for 3 days instead of being stored in a constant temperature andhumidity vessel, and both were then subjected to final sinteringtreatment as in Example 1. The test results are shown in Table 2 whereinthe sintered body treated with acetic anhydride vapor showed betterphysical properties as compared to the sintered body not heated withacetic anhydride vapor.

Table 2 sintered body treated with acetic anhydride sintered body nottreated with acetic anhydride EXAMPLE 8 A WC-Co powder mixture producedin the same manner as in Example 6 was compressed to form a 16 mm cubeand a bending strength test piece. These materials were prelimarysintered at 700C for 30 minutes in a H gas atmosphere, and cooledtherein to room temperature. Since the obtained preliminarily sinteredbody would be easily oxidized, acrylic acid monomer vapor (vaporpressure 200 mm Hg) was introduced into the H gas atmosphere for 30 min.at room temperature to adhere the vapor to the preliminarily sinteredbody in the H gas atmosphere. The amount of acrylic acid adhered wasabout 0.6 wt.%. The preliminarily sintered body thus treated was kept ina constant temperature and humidity vessel under the same conditions asin Example 6, and then vacuum sintered at 1,400C for 1 hour and 0.01 mmHg pressure.

Another preliminarily sintered body not treated with acrylic acid(monomer) vapor was also subjected to final sintering treatment in thesame manner.

The physical properties of both sintered bodies are shown in Table 3.

The trends indicated in the present example basically follow thediscussion regarding Example 6. However, with acrylic acid a preferredvapor pressure will be in the range of from about 50 to about 300 mm Hg,with the tendency being to utilize vapor pressures near the higher endof this range. Seldom would one use vapor pressures as low as about mmHg for the reasons advanced in Example 6.

In a manner similar to that in Example 6 the temperature and time oftreatment can vary, with generally temperatures in the area of roomtemperatures being used, though higher temperatures, e.g., 40 to about100C, can be used. With acrylic acid usually operation will be at atemperature less than about 150C.

The time of operation is selected in accordance with the principles setout in Example 6, with generally operations for about one half hourbeing selected as providing an adequate safety factor and yet not undulyincreasing the hold time in the apparatus.

As shown in the earlier embodiments where acrylic acid as used, ascompared to acetic acid, or butyric acid, the tendency will be to adheresomewhat greater amounts of acrylic acid, but usually an amount of fromabout 0.3 to about 1.2 weight percent adhered acrylic acid is sufficientfor ordinary commercial practices. Usually one would not adhere aslittle as about 0.2

weight percent in order to provide a safety factor for the operation.

EXAMPLE 9 A preliminarily sintered body formed as in Example 6 wastreated with acrylic acid (monomer) or a like carboxylic acid in lieu ofacetic anhydride, and subjected to the final sintering treatment asdescribed in Example 6. Carbon analysis of the thus obtained sinteredbodies showed that sintered bodies treated with carboxylic acid werescarcely oxidized and the decrease of the carbon content of the latterwas low, whereas a sintered body not treated with a carboxylic acidshowed greatly increased oxidation and the reduction of the carboncontent was also great, as shown in Table 4.

Whether the carboxylic acid or the anhydride thereof is fully penetratedinto the pores of the intermediate sintered body to prevent itsoxidation can be ascertained by cutting the sintered body aftertreatment and exposing the latter to an oxidizing atmosphere at hightemperature and high humidity.

The action of various carboxylic acids or anhydrides thereof arecompared below.

EXAMPLE 10 A compressed body produced from a WC5% Co alloy powder wassubjected to preliminary sintering at 700C under 0.03 mm Hg vacuum.Then, the preliminarily sintered body was cooled to C while undervacuum. Then, a carboxylic acid vapor at 100C (or the anhydride thereof)selected from acetic acid, acetic an hydride, acrylic acid, propionicacid, butyric acid, propionic anhydride, isovaleric acid, crotonic acid,caproic acid and benzoic acid was introduced into the H gas atmosphere.

To test the action of each carboxylic acid or the anhydride thereof, twocompressed powder bodies (cubes having 40 mm X 40 mm X 40mm size) wereused as specimens. One of the specimens after being presintered was cutinto two halves. Then, a pair of cut specimens, the uncut specimentreated by the carboxylic acid and another standard specimen not treatedwith the carboxylic acid (non-treated specimen) were charged into aconstant temperature humidity vessel kept at 40C and 90% moisture forhr., taken out of the vessel and vacuum-sintered at 1,450C, for 1 hr.under 0.01 mm Hg vacuum. The results of carbon analysis of the sinteredbodies obtained are shown in Table 5.

It will be apparent from Table 5 that the carbon content of the sinteredbody decreases as the oxidation thereof. Assuming that the carboncontent of the uncut specimen is indicated as A and that of theuntreated specimen is indicated as C, the large A-C value means that theoxidation inhibiting action of the corresponding carboxylic acid or theanhydride thereof used is strong. On the other hand, assuming that thecarbon content of the cut specimen is indicated as B, a small A-B valuemeans that the action of the corresponding carboxylic acid or theanhydride thereof to prevent the oxidation of the interior of thesintered body is strong. Therefore, a carboxylic acid or the anhydridethereof showing a large A-C value and a small A-B value is favorable.

molecular weight of less than 200 or an anhydride thereof to a startingpowder of a Group lV-a, Group V-a or Group VI-a metal, a powder of analloy containing such metals or a solid solution containing said metal,or a powder of a carbide of said metal.

2. A process for producing an intermediate product in the formation of acemented carbide characterized by adhering an unsubstituted carboxylicacid having a molecular weight of less than 200, or an anhydride Table 5carboxylic acid or the anhydride thereof A B C A-C A-B name boilingpoint molecular weight acetic acid 118C 60.05 5.56 5.56 4.57 0.99 0.00

acetic 140 102.06 5.51 5.48 4.55 0.96 0.03 anhydride acrylic acid 14172.06 A 5.59 5.59 4.57 1.02 0.00

propionic 141 74.08 5.53 5.51 4.57 0.96 0.02 acid butyric: acid 16288.10 5.47 5.31 4.57 0.82 0.21

propionic 168 130.16 5.39 5.18 4 57 0.82 0 21 anhydride isovaleric 174102.13 5.42 5.25 4.56 0.86 0.17 acid crotonic 189 86.09 5.43 5.30 4.560.87 0.13 acid caproic 206 116.16 5.36 5.13 4 55 0.81 0 23 acid benzoic250 122.12 5.32 5.06 4.57 0.75 0.26 acid It will be understood fromTable 5 and the drawing that a carboxylic acid or the anhydride thereofhaving a molecular weight of less than 200, especially acetic acid,acetic anhydride, acrylic acid or propionic acid,

exhibit a large A-C value and a small A-B value and are 4 most suitablefor use.

Although the effect of the carboxylic acid or the anhydride on thetreatment of the starting powder or the intermediate sintered body isprimarily influenced by the molecular weight of the acid or theanhydride, the 45 value of the boiling point also has an influence onthe treatment.

In any case, the oxidation of (1 a starting powder for the super hardalloy, (2) a mixture of the starting powder, (3 a powder compressed bodyor (4) an intermediate sintered body can be prevented by adheringthereto a carboxylic acid having a molecular weight of less than 200, orthe anhydride thereof. Therefore a cemented carbide having a desiredcarbon content can be produced irrespective of the length of the timeperiod required for producing the latter or storing and shipping anintermediate product, without the use of any particular atmosphere gasor apparatus.

While the invention has been described in detail and I with reference tospecific embodiments thereof, it will thereof, to a powder of a GroupVIII metal or a powder of an alloy containing said metal.

3. A process for producing an intermediate product in the formation of acemented carbide, according to the claim 1 characterized by adhering theunsubstituted carboxylic acid or anhydride thereof, in the vaporizedstate, to the starting powder immediately after preparation thereof.

4. A process for producing an intermediate product in the formation of acemented carbide characterized by adhering an unsubstituted carboxylicacid having a molecular weight of less than 200, or an anhydridethereof, to a powder mixture containing both: (a) one or more powders ofa Group lV-a, Group V-a or Group Vl-a metal, a powder of an alloy or asolid solution containing such a metal or a powder of a carbide of sucha metal, and (b) one or more powders of Group VIII metal or an alloythereof.

5. A process for producing an intermediate product according to claim 4characterized in that the unsubstituted carboxylic acid or an anhydridethereof is adhered to the starting powder by adding the unsubstitutedcarboxylic acid or the anhydride thereof to a wet- 0 ting solution formixing the powders.

6. A process for producing an intermediate product in the production ofa cemented carbide characterized by compressing a powder mixturecontaining: (a) one or more powders of a Group IV-a, Group V-a or GroupVl-a metal, a powder of an alloy or a solid solution containing such ametal, and (b) one or more powders of a Group VIII metal and a powder ofan alloy thereof, and adhering an unsubstituted carboxylic acid having amolecular weight of less than 200 or an anhydride thereof to theresultant compressed powder body.

7. A process for producing an intermediate product according to theclaim 6 characterized in that the adherence of the unsubstitutedcarboxylic acid or the anhydride thereof to the compressed powder bodyis carried out by exposing the compressed powder body to the gaseouscarboxylic acid or anhydride thereof.

8. A process for producing an intermediate product in the formation of acemented carbide characterized by compressing a powder mixturecontaining (a) one or more powders of a Group IV-a, Group V-a or GroupVI-a metal, a powder of an alloy or a solid solution containing such ametal; and (b) one or more powders of Group VIII metal or a powder of analloy thereof, subjecting the resultant compressed powder body topreliminary sintering at a temperature lower than the final sinteringtemperature, and then adhering an unsubstituted carboxylic acid having amolecular weight of less than 200 or an anhydride thereof to theobtained preliminarily sintered body, which sintered body has fine poresin the surface thereof.

9. A process for producing an intermediate product according to claim 8characterized in that the adherence of the unsubstituted carboxylic acidor the anhydride thereof to the intermediate sintered product is carriedout by introducing gaseous carboxylic acid or the anhydride thereof intoan intermediate sintering zone to penetrate the gas into the fine poresof the preliminarily sintered body.

10. In a process for producing cemented carbides comprising one or morecarbides of a Group IV-a, V-a or VI-a metal and one or more metals fromGroup VIII involving a high temperature sintering operation, theimprovement wherein the components of the cemented carbide are, in atleast one processing sequence prior to final sintering, contacted withan unsubstituted carboxylic acid or anhydride thereof having a molecularweight less than 200, whereby oxidation is prevented.

11. In a process for producing cemented carbides comprising one or morecarbides of a Group IV-a, V-a or VI'a metal and one or more metals fromGroup VIII by wet mixing and drying a starting powder of said carbidesto form a mixture powder, pressing said mixture powder to form a formedbody, optionally preliminarily sintering said formed body, and finallysintering said formed body, the improvement comprising applying anunsubstituted carboxylic acid or an anhydride thereof having a molecularweight less than 200 on an oxidizable material used to produce saidcemented carbide to prevent oxidation.

12. A process comprising contacting an oxidizable material used in theproduction of cemented carbides by wet mixing and drying a startingpowder of said carbides to form a mixture powder, pressing said mixturepowder to form a formed body, optionally preliminarily sintering saidformed body, and finally sintering said formed body, said materialcomprising a Group lV-a, V-a, VI-a or VIII metal, or a Group IV-a, V-aor VI-a carbide or a carbide solid solution, with an unsubstitutedcarboxylic acid or an anhydride thereof having a molecular weight ofless than 200 to prevent oxidation of said material.

13. An intermediate product used in the formation of a cemented carbidecomprising,

a starting powder of a Group IV-a, Group V-a or Group VI-a metal, apowder of an alloy containing such metals or a solid solution containingsaid metal, or a powder of a carbide of said metal having adheredthereto an unsubstituted carboxylic acid having a molecular weight ofless than 200 or an anhydride thereof.

14. An intermediate product used in the formation of a cemented carbidecomprising, a powder mixture containing both:

a. one or more powders of a Group IV-a, Group V-a of Group VI-a metal, apowder of an alloy or a solid solution containing such a metal or apowder of a carbide of such a metal, and

b. one or more powders of Group VIII metal or an alloy thereof havingadhered thereto an unsubstituted carboxylic acid having a molecularweight of less than 200, or an anhydride thereof.

15. An intermediate product used in the formation of a cemented carbidecomprising, a formed body containing:

a. one or more powders of a Group IV-a, Group V-a or Group VI-a metal, apowder of an alloy or a solid solution containing such a metal, and

b. one or more powders of a Group VIII metal or a powder of an alloythereof having adhered thereto an unsubstituted carboxylic acid having amolecular weight ofless than 200, or an anhydride thereof.

16. An intermediate product used in the formation of a cemented carbidecomprising,

a preliminarily sintered body having fine pores in the surface thereof,said body containing a. one or more powders of a Group VI-a, Group V-aor Group VI-a metal, a powder of an alloy or a solid solution containingsuch a metal, and

b. one or more powders of a Group VIII metal or a powder of an alloythereof having adhered thereto an unsubstituted carboxylic acid having amolecular weight of less than 200, or an anhydride thereof.

17. The process of claim 11, wherein said applying is in a non-oxidizingatmosphere or in a vacuum.

1. S PROCESS FOR PRODUCING AN INTERMEDIATE PRODUCT IN THE FORMATION OF ACEMENTED CARBIDE CHARACTERIZED BY ADHERING AN UNSUBSTITUTED CARBOXYLICACID HAVING MOLECULAR WEIGHT OF LESS THAN 200 OR AN ANHYDRIDE THEREOF TOA STARTING POWDER OF A GROUP IV -A, GROUP V1-A METAL, A POWDER OF ANALLOY CONTAINING SUCH METALS OR A SOLID SOLUTION CONTAINING SAID METAL,OR POWDER OF A CARBIDE OF SAID METAL.
 2. A process for producing anintermediate product in the formation of a cemented carbidecharacterized by adhering an unsubstituted carboxylic acid having amolecular weight of less than 200, or an anhydride thereof, to a powderof a Group VIII metal or a powder of an alloy containing said metal. 3.A process for producing an intermediate product in the formation of acemented carbide, according to the claim 1 characterized by adhering theunsubstituted carboxylic acid or anhydride thereof, in the vaporizedstate, to the starting powder immediately after preparation thereof. 4.A process for producing an intermediate product in the formation of acemented carbide characterized by adhering an unsubstituted carboxylicacid having a molecular weight of less than 200, or an anhydridethereof, to a powder mixture containing both: (a) one or more powders ofa Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or asolid solution containing such a metal or a powder of a carbide of sucha metal, and (b) one or more powders of Group VIII metal or an alloythereof.
 5. A process for producing an intermediate product according toclaim 4 characterized in that the unsubstituted carboxylic acid or ananhydride thereof is adhered to the starting powder by adding theunsubstituted carboxylic acid or the anhydride thereof to a wettingsolution for mixing the powders.
 6. A process for producing anintermediate product in the production of a cemented carbidecharacterized by compressing a powder mixture containing: (a) one ormore powders of a Group IV-a, Group V-a or Group VI-a metal, a powder ofan alloy or a solid solution containing such a metal, and (b) one ormore powders of a Group VIII metal and a powder of an alloy thereof, andadhering an unsubstituted carboxylic acid having A molecular weight ofless than 200 or an anhydride thereof to the resultant compressed powderbody.
 7. A process for producing an intermediate product according tothe claim 6 characterized in that the adherence of the unsubstitutedcarboxylic acid or the anhydride thereof to the compressed powder bodyis carried out by exposing the compressed powder body to the gaseouscarboxylic acid or anhydride thereof.
 8. A process for producing anintermediate product in the formation of a cemented carbidecharacterized by compressing a powder mixture containing (a) one or morepowders of a Group IV-a, Group V-a or Group VI-a metal, a powder of analloy or a solid solution containing such a metal; and (b) one or morepowders of Group VIII metal or a powder of an alloy thereof, subjectingthe resultant compressed powder body to preliminary sintering at atemperature lower than the final sintering temperature, and thenadhering an unsubstituted carboxylic acid having a molecular weight ofless than 200 or an anhydride thereof to the obtained preliminarilysintered body, which sintered body has fine pores in the surfacethereof.
 9. A process for producing an intermediate product according toclaim 8 characterized in that the adherence of the unsubstitutedcarboxylic acid or the anhydride thereof to the intermediate sinteredproduct is carried out by introducing gaseous carboxylic acid or theanhydride thereof into an intermediate sintering zone to penetrate thegas into the fine pores of the preliminarily sintered body.
 10. In aprocess for producing cemented carbides comprising one or more carbidesof a Group IV-a, V-a or VI-a metal and one or more metals from GroupVIII involving a high temperature sintering operation, the improvementwherein the components of the cemented carbide are, in at least oneprocessing sequence prior to final sintering, contacted with anunsubstituted carboxylic acid or anhydride thereof having a molecularweight less than 200, whereby oxidation is prevented.
 11. In a processfor producing cemented carbides comprising one or more carbides of aGroup IV-a, V-a or VI-a metal and one or more metals from Group VIII bywet mixing and drying a starting powder of said carbides to form amixture powder, pressing said mixture powder to form a formed body,optionally preliminarily sintering said formed body, and finallysintering said formed body, the improvement comprising applying anunsubstituted carboxylic acid or an anhydride thereof having a molecularweight less than 200 on an oxidizable material used to produce saidcemented carbide to prevent oxidation.
 12. A process comprisingcontacting an oxidizable material used in the production of cementedcarbides by wet mixing and drying a starting powder of said carbides toform a mixture powder, pressing said mixture powder to form a formedbody, optionally preliminarily sintering said formed body, and finallysintering said formed body, said material comprising a Group IV-a, V-a,VI-a or VIII metal, or a Group IV-a, V-a or VI-a carbide or a carbidesolid solution, with an unsubstituted carboxylic acid or an anhydridethereof having a molecular weight of less than 200 to prevent oxidationof said material.
 13. An intermediate product used in the formation of acemented carbide comprising, a starting powder of a Group IV-a, GroupV-a or Group VI-a metal, a powder of an alloy containing such metals ora solid solution containing said metal, or a powder of a carbide of saidmetal having adhered thereto an unsubstituted carboxylic acid having amolecular weight of less than 200 or an anhydride thereof.
 14. Anintermediate product used in the formation of a cemented carbidecomprising, a powder mixture containing both: a. one or more powders ofa Group IV-a, Group V-a of Group VI-a metal, a powder of an alloy or asolid solution containing such a metal or a powder oF a carbide of sucha metal, and b. one or more powders of Group VIII metal or an alloythereof having adhered thereto an unsubstituted carboxylic acid having amolecular weight of less than 200, or an anhydride thereof.
 15. Anintermediate product used in the formation of a cemented carbidecomprising, a formed body containing: a. one or more powders of a GroupIV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solidsolution containing such a metal, and b. one or more powders of a GroupVIII metal or a powder of an alloy thereof having adhered thereto anunsubstituted carboxylic acid having a molecular weight of less than200, or an anhydride thereof.
 16. An intermediate product used in theformation of a cemented carbide comprising, a preliminarily sinteredbody having fine pores in the surface thereof, said body containing a.one or more powders of a Group VI-a, Group V-a or Group VI-a metal, apowder of an alloy or a solid solution containing such a metal, and b.one or more powders of a Group VIII metal or a powder of an alloythereof having adhered thereto an unsubstituted carboxylic acid having amolecular weight of less than 200, or an anhydride thereof.
 17. Theprocess of claim 11, wherein said applying is in a non-oxidizingatmosphere or in a vacuum.